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Scanning Vibrometer C5 Hardware and Software Module of the KLIPPEL ANALYZER SYSTEM (Document

Revision 2.1)

FEATURES

Measures geometry and mechanical vibration of the transducer

Visualizes the vibration behavior

Shows contribution to sound pres‐sure output

Predicts directivity pattern

Separates radial and circular modes

Analyzes actively radiating cone re‐gions

Detects loudspeaker defects

Scanning Vibrometer 1 Principle C5

KLIPPEL Analyzer System of 30

CONTENT

1 Principle .......................................................................................................................................................... 3

2 SCN Vibrometer .............................................................................................................................................. 4

3 SCN Analysis Software .................................................................................................................................... 7

3.1 Sound Radiation .................................................................................................................................. 10

3.2 Analysis and Decomposition ................................................................................................................ 10

3.3 Data Import and Export ....................................................................................................................... 12

4 SCN Import / Export Interface ...................................................................................................................... 13

5 SCN Radiation Area SD ................................................................................................................................. 17

6 SCN Sound Power / Directivity ..................................................................................................................... 18

7 Typical Configurations .................................................................................................................................. 18

8 Limits ............................................................................................................................................................ 19

8.1 DUT ...................................................................................................................................................... 19

8.2 Scanning Hardware rev. 2.0 ................................................................................................................. 20

8.3 Motor Control ...................................................................................................................................... 23

8.4 Setup Parameter of Scanner ................................................................................................................ 23

8.5 Vibration and Radiation Analysis (Results) .......................................................................................... 24

8.6 Setup Parameter Analyzer ................................................................................................................... 26

9 Diagnostics ................................................................................................................................................... 27

10 Evaluation ..................................................................................................................................................... 30

11 References .................................................................................................................................................... 30

The Scanning Vibrometer (SCN) performs a non‐contact measurement of the mechanical vibration and the geometry data of cones, diaphragms, panels and enclosures. One rotational and two linear actuators (φ, r, z) move a laser displacement sensor over a user‐defined grid. At each measurement point the transducer is excited by a stimulus giving sufficient spectral resolution and high SNR in the measured response over the whole audio band (< 25 kHz). The collected data can be analyzed with‐in the SCN software or exported to other FEA/BEA applications for further processing. Modern techniques of image processing are used for enhancing relevant information, suppressing noise and animating the vibration as a stroboscopic video. The sound pressure output in the far field and the directivity pattern are calculated and the contribution of each vibrating point on the vibrating sur‐face is visualized. The software indicates critical vibration pattern and uses decomposition tech‐niques for separating radial and circular modes.

Article Numbers:

2510‐001

2510‐010/2510‐011 (USB Dongle)

2510‐020

2510‐030

2510‐040

SCN Vibrometer

SCN Analysis Software

SCN Import/Export Interface

SCN Radiation Area SD

SCN Sound Power / Directivity

Scanning Vibrometer 1 Principle C5


1 Principle

Stimulus

ControlHardware

SignalAquisition

Scanner

Sensor

Transducer

Amplifier

H(s,r)

ExternalFEA-Software

SCNANALYSIS SOFWARE

MeasuredVibration

PredictedVibration

MeasuredGeometry

MaterialParameters

SPLresponse

VibrationModes

directivityVibration

components

The SCN Vibrometer is dedicated to loudspeakers, micro‐speakers, headphones and other electro‐acoustical or electro‐mechanical transducers. The Vibrometer uses standard modules of the KLIPPEL R&D System such as a displacement triangulation laser sensor, the Distortion Analyzer DA2 and the Transfer Function Module (TRF) to excite the loudspeaker under test with a pre‐shaped sweep and to perform the signal acquisition and spectral analysis. The scanning hardware uses a turntable with two additional linear actuators and control hardware to scan the target surface in polar coordinates. The scanning vibrometer provides vibration data and the cone geometry to the SCN Analysis Soft‐ware which performs visualization, animation of the mechanical vibration and the prediction of the sound pressure output at any point in the half‐space sound field. Novel decomposition techniques show radial and circular modes and vibration components related to the SPL output. It is the target of the analysis to provide a better understanding of the interaction between vibration and radiation. The SCN Import/Export Interface (an add‐on of the KLIPPEL Scanning Vibrometer) provides the measured cone geometry and vibration data for further processing with any third‐party software. This may be useful to check the geometrical variations in quality control and to investigate design choices by performing a vibration and radiation analysis based on FEA or BEA. The material parame‐ter measurement module MPM of the KLIPPEL R&D Software provides the E modulus and loss factor of the cone and suspension material.

Scanning Vibrometer 2 SCN Vibrometer C5


2 SCN Vibrometer

3D Scanner

φ

r

z

transducer sensor

Mechanical scanning system with one rotational (φ) and two linear actuators (r, z).

Most electro‐acoustical transducers use a single motor which excites the diaphragm, cone or panel in one di‐rection (z dimension). Thus the meas‐urement of the displacement in this direction can be accomplished by using a displacement sensor scanning 2 dimensions (radius r and angle φ) of the target surface. The transducer under test is rotated by a turn table (φ coordinate) and shifted by a linear actuator (r coordinate). An additional actuator is required to adjust the laser to the optimal distance Vd in the z dimension.

Motor Control

The Motor Control is the hardware control unit for the 3D Scanner. Con‐necting a computer via USB‐interface the Scanning and Visualization Soft‐ware (SCN) can be used to control the unit and gather measuring results for the following visualization. The inte‐grated microprocessor provides state information of the Scanning Hard‐ware for the software and controls the 3 build in stepper motor drivers for actuating each agitation axis.

Displacement Sensor

Displacement sensor based on the

triangulation principle

Optical measurement of loudspeaker cone vibration (scanning vibrometry) can also be accomplished by using Laser triangulation technique which is a cost effective alternative to Doppler interferometry. Since triangulation sensors provide primarily displacement, advanced signal processing is required to meas‐ure the break‐up modes up to 25 kHz at sufficient signal to noise ratio. The voice coil displacement decreases with 12 dB per octave above reso‐nance frequency where the mass is dominant. Thus a sinusoidal sweep with constant voltage generates xpeak(fs)= 1mm at the resonance fre‐quency fs = 20 Hz but would produce only 10‐6 mm (1nm) peak displace‐ment at 20 kHz.



Shaping of the Stimu‐lus

-10

-5

0

5

10

0 10 20 30 40 50 60 70 80

[V]

Time [ms]

Stimulus (t)

Shaped logarithmic sinusoidal

sweep

KLIPPEL

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50 60 70 80

[mm

][e-3

]

Time [ms]

Y2 (t)

Averaged displacement signal

The decay of the displacement above resonance frequency can be compen‐sated by using a stimulus where the higher frequency components are emphasized inversely. The amplitude is not constant but rises quadratically with frequency from 0.1 mV up to 10 V rms. Repeating the measurements with the same stimulus 2n times and aver‐aging the measured displacement responses will improve the signal to noise ratio by 3*n dB. Due to the shaping of the stimulus the displacement at the resonance (about 100 Hz) is in the same order of magnitude (about 0.5 μm) as at high frequencies. The noise floor stays at 5nm giving sufficient signal to noise ratio (> 40 dB)

Displacement Transfer Function KLIPPEL

-610

-510

-410

-310

-210

-110

500 1k 2k 5k 10k

[mm

/ V

]

Frequency [Hz]

surround dust cap

Tr

ansfer function |Hx(s)| measured

at the dust cap and at the sur‐

round

Due to the shaping of the stimulus the output signal of the triangulation laser corresponds with the accelera‐tion of the target point. Since the shaping is not relevant for further analysis it is more convenient to cal‐culate the transfer function Hx(s,r)=X(s)/U(s) by referring the dis‐placement X(s) to the voltage U(s) of the stimulus (0dB=1mm/V).

Grid and scanning path

The scanning starts at the outside rim and proceeds inwards.

The target is scanned in polar coordi‐

nates (r, ) due to the turntable and the radial actuator used. The grid can be generated automati‐cally or manually to provide sufficient resolution at areas of particular inter‐est. The scanning process can be per‐formed in sequential steps

a) profile scan at constant an‐

gle (50 points)

b) explore scan (450 Points)

c) detailed scan (3200 Points)

Scanning Modes The height of the laser sensor is automatically adjusted during the scan‐ning process according to the following modes

Normal Scan

In this mode the optimal height of the laser head is calculated



from the geometry of the target object identified during the scan‐

ning process. In this mode the laser follows the slope of the cone

profile and makes it possible to measure a dust cap which is at a

much lower position than the surround. This mode assumes that

the cone angle is lower than 60 degree and there are no steps

larger than 20 mm. This mode works for most transducers and is

recommended for woofer systems.

Flat Scan

In this mode the vertical position of the laser head is not changed

during the scanning. This mode gives the highest accuracy in

measured geometry. It is recommended for tweeters, micro‐

speakers, panels where the geometry varies less than 10 mm.

Floating Scan

In this mode the vertical position of the laser will always stay

above a minimal value. This mode is required to measure the vi‐

brations of transducers operated in a vacuum chamber where a

glass plate is placed between target and laser head.

Furthermore the specification of certain dangerous scanning radii can be used to locate critical spots on the cone for the normal and floating scan‐ning mode. At these dangerous radii the vertical position of the laser will only be adjusted to absolutely safe values.

Geometry Measure‐ment

A particular scanning mode is provided for measuring the geometry only. Hereby no excitation of the transducer is required and the total measure‐ment time can be significantly reduced.

Configuration The SCN Vibrometer comprises the following components:

3D Scanner (3 actuators move the displacement sensor in polar

coordinates)

Scanning Control Hardware

Scanning Control Software

Cables

Other modules of the KLIPPEL R&D SYSTEM

Laser‐DisplacementSensor (see A2 Laser Displacement Sensor)

Distortion Analyzer DA2

TRF Transfer Function Module

Additional equipment:

Power Amplifier

Scanning Vibrometer 3 SCN Analysis Software C5


3 SCN Analysis Software

The SCN Analysis Software is optimized for the visualization of the vibration data of loudspeaker cones. This software only requires the results (data file) of the SCN Vibrometer. The software is free for the visualization of digitally signed scan data by Klippel, for other data files a license is required.

Data Processing The measured vibration and geometry data is prepared for an optimal visualiza‐tion: INTERPOLATION: The optical resolution can be increased by interpolating between the measured points.

a) original data (744 points), b) interpolated data (2000 points) c) interpolated

points (10000 points), d‐f) Shaded versions of the pictures above



SMOOTHING:

Noise in the vibration data can be suppressed by applying two‐dimensional

smoothing:

a) original vibration , b) medium smoothing c) maximal smoothing

ERROR CORRECTION:

Measurement errors can be detected and removed by a correlation tech‐

nique.

a) original vibration data, b) applying the error correction c) applying smoothing

d) increased visual resolution

3D Animation From the measured geometry a three‐dimensional representation of the cone is created and the vibration at each measurement point is illustrated as an offset superposing the pure cone geometry. By rotating the vibration phase around the unit circle at each measurement point a continuous animation of the cone motion is created. The amplitude of the superposing offset can be manually increased to visually emphasize small vibrations.



geometry only

geometry with low vibration

enhanced vibration

Coloration Schemes

The color of the three‐dimensional cone surface can be used to display different vibration properties. It is possible to choose coloration according to the instan‐taneous amplitude or according to the instantaneous phase of the vibrating points. Monochrome representations can also be selected for easier printing.

Blue and red colors represent positive and negative displacement (phase), re‐spectively, color intensity represents relative displacement (amplitude)

Yellow and red colors represent positive and negative displacement (phase only)

2D plots A 2D plot is provided where the vibration data are projected on the measured geometry. A cursor may be used to locate critical vibration modes and to meas‐ure the distances between nodes in mm.

The vibration amplitude is represented as blue color intensity revealing areas of minimal and maximal vibration (nodes).

The phase of the vibration is repre‐sented as yellow and red colors

Vibration of the Cone Profile

A two‐dimensional plot shows the profile of the measured target surface for any

angle (0 < < 360 o) in mm and the overlaid vibration pattern. Modes of vibra‐tion and the position of nodes can be determined more easily.

r = 0.0 mm, phi = 0.0° Vibration of one point on the cone

A cursor (blue bar) in the Cone Profile may be used to select a point of the cone and to show the measured displacement transfer function Hx in mm per Volt.



-100

-90

-80

-70

-60

-50

-40

-30

-20

103 104

Displacement Transfer Function - Point 3151

Hx

[dB

]

Frequency [Hz]

3.1 Sound Radiation

Frequency Re‐sponse

55

60

65

70

75

80

103 104

Total Sound Pressure Level

SP

L [

dB

]

Frequency [Hz] Using the geometry and the vibration data the SPL response is predicted in the

far‐field at the point r(ro,, ) on the basis of the Rayleigh equation. Directivity Pattern The sound pressure modeling can also

be used to evaluate the directivity of the sound radiation.

For a certain selected frequency the total sound pressure at certain points on a hemisphere over the cone is de‐termined and displayed in a polar plot.

3.2 Analysis and Decomposition

Radial and circu‐lar modes



Total component

The cone vibration can be separated into single components with special rele‐vance for the analysis by novel data decomposition techniques. The total vibra‐tion is divided into a radial component and a circumferential component. Each of them can be analyzed separately. The sound pressure produced by the re‐spective component can be regarded independently, too.

circradtotal xxx

Radial component

Circular component

Decomposition related to the sound pressure output

A second decomposition technique is capable of separating vibration compo‐nents according to their contribution to the total sound pressure at a certain

listener position r(ro,,).

ofoutantiintotal xxxx

In‐phase

Component

Anti‐Phase

Component

Quadrature

Component

The in‐phase component of the vibration contributes to the sound pressure at the listening point. The anti‐phase component of the vibration reduces the sound pressure output. The quadrature component produces positive and nega‐tive volume velocity which cancels out in the near field and will not contribute to the total sound pressure at the listening position.

r(ro,,)

SPL

radiation

TOTAL

VIBRATION



The SPL frequency response of the total output can be compared with the in‐phase and anti‐phase component.

KLIPPEL

0

10

20

30

40

50

60

70

80

103 104

Total SPL In-Phase Component Anti-Phase Component

The dashed anti‐phase component in the diagram above produces a very low SPL output before the cone breaks up (< 2 kHz). At 6 kHz the anti‐phase compo‐nent almost equals the in‐phase component causing a dip in the total SPL out‐put at the listener position.

Acceleration Level Looking at the accumulated acceleration level of the cone surface motion is a good indication for the Eigen frequencies (Natural Frequencies) and the me‐chanical damping of the cone's Eigen modes (Natural Modes). The total acceler‐ation level is shown in relation to the total sound pressure level to allow a quick comparison of true cone vibration and the actual sound radiation. The acceleration level can be combined with the decomposition technique to investigate i.e. the vibration level of the quadrature component, which does not produce sound but still comprises a certain amount of vibration energy.

KLIPPEL

0

10

20

30

40

50

60

70

80

90

2*102 4*102 6*102 8*102 103 2*103 4*103 6*103 8*103

SCN Result Curves

SP

L [dB

]

f [Hz]

Total SPL Acceleration Level Quadrature Acceleration

The in‐phase and anti‐phase components are always equal in acceleration level

and sound pressure level.

3.3 Data Import and Export

Scan Data All results from the scanning process (Vibration Data, Cone Geometry, status information) are stored in KLIPPEL SCN Format and are the basis for performing an SCN Analysis.

All Curves to dB‐Lab

Export of all result curves of the SPL modeling and the acceleration level into a Klippel Database file which can be opened using the Klippel dB‐Lab.

Single Curve Export of vibration amplitude and modeled sound pressure curves in a text

Scanning Vibrometer 4 SCN Import / Export Interface C5


based format which can be easily imported into SCILAB / MATLAB and the dB LAB software by KLIPPEL by using the clipboard.

Pictures and Mov‐ies

All graphical objects can be exported as single pictures (bmp, jpg, png, vector‐graphics) or in case of an animation as a movie file. Thereby a compressed vid‐eo stream is created and saved in the AVI video format which can be watched using any common movie player software.

Export and Import of Geometry and Vibration Data

The geometry of the scanned surface (in polar or cartesian Coordinates) and the vibration data (transfer function between terminal voltage and displace‐ment at point r) can be exported and imported by using the module SCN Im‐port/Export Interface.

4 SCN Import / Export Interface

High precision Geometry Scan‐ning

The module Import/Export Interface is an optional Add‐On for the SCN Analysis Software. It provides access to the geometry of a 3D object scanned from one side at high precision. This data is very useful for loudspeaker development and quality control. Here some examples:

1. Measuring the shape of loudspeaker parts (cones, horn geometries)

where no specification is available

2. Checking the geometry of a prototype in R&D and production samples

in Quality Control

3. Providing input for BEA and analyzing output from FEA

Geometry Export Export of the measured geometry in high precision.

Three different DXF (Drawing Exchange Format) export options are supported:

1. 3D Faces: All points are connected to a mesh to reproduce the surface

of the measured cone.

2. Lines: The surface of the cone is given by single lines connecting the

measured points

3. Points: Only the measured points are included in the DXF export

There is also the option of exporting the geometry in STL (stereo lithography) format.

Geometry and Vibration Export

Geometry and vibration data can be exported into text file in ASCII format. The data may be used for enhanced sound radiation modeling (BEA) and any other kinds of post processing. The geometry may be provided in Polar Coordinates

(angle , radius r, height z) or in Cartesian Coordinates (x,y,z). The vibration data is provided as a transfer functions Hx(f)=X(f)/U(f) between voltage U(f) in Volt at the terminals and displacement X(f) in mm at each measured point. The transfer function consists of an amplitude response (0dB = 1mm /V) and the phase re‐sponse (rad).

These are the following options:

1. Export of the Raw Data: The original data is provided without applying

any kind of correction.

2. Export of the Interpolated Data: The SCN Analysis Software is used to



interpolate missing data points, for smoothing the data and for apply‐

ing error correction if an optical error is identified.

EXAMPLE:

;Klippel 3D Scanner Data

;driver.asc

;Created: 20.05.2008 15:17:15

;##########################################

;Measurement Points (geometry)

;Format: i x_i y_i z_i

;i = point number from 1 to n

;x_i = coord x of point i in millimeter (accuracy 0.05mm)

;y_i = coord y of point i in millimeter (accuracy 0.05mm)

;z_i = height of point i in millimeter (accuracy 0.05mm)

;

1 0 0 4.1

2 0 2.5 4.25

3 ‐0.65 2.41 4.15

4 ‐1.25 2.17 4.05

5 ‐1.77 1.77 3.9

6 ‐2.16 1.25 3.8

7 ‐2.41 0.65 3.7

8 ‐2.5 0 3.65

9 ‐2.41 ‐0.65 3.6

10 ‐2.17 ‐1.25 3.55

;

;############################

;Measurement Data

;Format: Frequency = fj

;Format: i x_i(f_j) p_i(f_j)

;i = point number from 1 to n

;x_i(f_j) = displacement amplitude of point i, frequency j in dB ‐ [mm/V]

;p_i(f_j) = displacement phase of point i, frequency j in Radian

;

Frequency=140.63

1 ‐7.124 ‐0.53407

2 ‐7.08 ‐0.52461

3 ‐7.058 ‐0.52497

4 ‐6.97 ‐0.53189

5 ‐7.224 ‐0.53094

6 ‐7.324 ‐0.52497

7 ‐7.271 ‐0.53329

8 ‐7.227 ‐0.52956

9 ‐7.268 ‐0.52895

10 ‐7.203 ‐0.53399

Frequency=187.5

1 ‐12.806 0.15132

2 ‐12.763 0.1524

3 ‐12.753 0.13918

4 ‐12.607 0.14999

5 ‐12.85 0.15638

6 ‐12.862 0.15395



7 ‐12.882 0.14751

8 ‐12.828 0.14894

9 ‐12.845 0.14988

10 ‐12.91 0.1522

A second export option is the generation of a text based file which can be pro‐cessed by SCILAB software. That Scilab Export File can also be imported again after individual post processing steps.

Geometry and Vibration Import

External geometry and vibration data can be imported for Analysis. That can be used to import data generated by simulation tools or by external measure‐ments. The import is based on a text file format which can be processed by SCILAB. Especially data which has been exported in Scilab Export File format can be di‐rectly imported again. Certain restrictions apply for a Scilab script to comply with the import function‐ality of the Klippel Scanning System.

EXAMPLE:

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// example file for producing valid scilab data for

// import into Klippel Scanning System 1.3

//

// Copyright by Klippel GmbH, Dresden, Germany ©2011

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// define required import constants

%SCN_FILE_VERSION = 1.1;

%SCN_COORDINATE_SYSTEM = "polar";

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// define geometry matrix:

// first column = point number

// second column = radius in [mm]

// third column = angle in [rad]

// fourth column = height in [mm]

//

// outer radius = 20mm

// regular polar grid with 17 points

geometry=[

1 0 0 0;

2 10 0 2;

3 10 1/4*%pi 2;

4 10 2/4*%pi 2;

5 10 3/4*%pi 2;

6 10 4/4*%pi 2;

7 10 5/4*%pi 2;

8 10 6/4*%pi 2;

9 10 7/4*%pi 2;

10 20 0 3;

11 20 1/4*%pi 3;



12 20 2/4*%pi 3;

13 20 3/4*%pi 3;

14 20 4/4*%pi 3;

15 20 5/4*%pi 3;

16 20 6/4*%pi 3;

17 20 7/4*%pi 3];

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// define three frequencies

frequency = [100;200;400];

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// define displacement amplitude:

// for each point specified in geometry array

// for each frequency

// amplitude given in dB [mm / V]

amplitude=[

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44;

‐20 ‐32 ‐44];

// ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

// define displacement phase:

// for each point specified in geometry array

// for each frequency

// phase given in [rad]

phase=[

0 0 0;

0 0 0;

0 1/4*%pi 1/4*%pi;

0 1/2*%pi 2/4*%pi;

0 1/4*%pi 3/4*%pi;

0 0 4/4*%pi;

0 7/4*%pi 5/4*%pi;

0 3/2*%pi 6/4*%pi;

0 7/4*%pi 7/4*%pi;

0 0 0;

0 1/4*%pi 1/4*%pi;

Scanning Vibrometer 5 SCN Radiation Area SD C5


0 1/2*%pi 2/4*%pi;

0 1/4*%pi 3/4*%pi;

0 0 4/4*%pi;

0 7/4*%pi 5/4*%pi;

0 3/2*%pi 6/4*%pi;

0 7/4*%pi 7/4*%pi];

5 SCN Radiation Area SD

Effective Radia‐tion Area SD

The application Radiation Area SD is an optional add‐on for the SCN Analysis Software. It provides an accurate result for the effective radiation area, particu‐larly for small drivers and asymmetric driver shapes. This application needs a separate license and requires only the results (data file) of the SCN Vibrometer. A scanning measurement with an appropriate number of measurement points on the diaphragm delivers the needed data. By dividing the total volume flow with a representative voice coil displacement a frequency dependent SD‐graph is obtained. That curve will be averaged over frequency. With an adjustable averaging frequency a very stable and significant value can be derived. The av‐eraging radius can be adjusted as well and is illustrated on the related driver plots.

Displacement transfer function Hx

By clicking the Option buttons the graph plot can be switched between the Sd‐ parameter curve and the averaged displacement transfer function Hx(f). The latter curve is yielded by a spatial averaging of all given displacement curves at a chosen radius. The averaged displacement curve is also used to obtain the SD(f) curve. After a calculation the data can be exported and reviewed in the Klippel dBLab.

Scanning Vibrometer 6 SCN Sound Power / Directivity C5


6 SCN Sound Power / Directivity

Sound Power

The Sound Power application is another optional add‐on for the SCN Analysis Software. It can calculate the sound power radiation into the half space without requiring a special acoustic room. The evaluation of the frequency dependent Sound Power is based on the Ray‐leigh integral. A reference voltage of 0.4V is used for the calculation which al‐lows a direct comparison of the Sound Power Level and the SPL in 1m distance. The Decomposition into the Sound Power contributions of radial and circular vibration components can be applied, as described above in the section SCN Analysis Software. After a calculation the data can be exported and reviewed in the Klippel dBLab.

Directivity Index The Directivity Index DI shows the ratio of the SPL on axis to the overall SPL av‐eraged in the half space.

Coverage Angle The Coverage Angle of the driver is calculated within an adjustable frequency range according to the IEC standard 60268‐5.

7 Typical Configurations

COMPONENTS REQUIRED SCANNING

+ ANALYSIS

ANALYSIS

ONLY

GEOMETRY

MEASUREMENT

Components of the Scanning Vibrometer

Scanning hardware (stand with turntable) x ‐ x

Scanning Vibrometer 8 Limits C5


Motor Control (Scanning control device) x ‐ x

Software modules

SCN Analysis Software x ‐ x

SCN Analysis Dongle Software ‐ x ‐

Additional Klippel‐R&D‐System Requirements

Distortion Analyzer Hardware (DA2) x ‐ x

TRF‐Module x ‐ x

Laser Keyence G32 / G82 / H052 x ‐ x

Dongle ‐ x ‐

Additional Requirements

Amplifier x ‐ x

8 Limits

8.1 DUT

Parameter Symbol Min Typ Max Unit

Maximal Diameter D 76 cm

Height H 33 cm

Mass M 70 kg

Vertical steps in DUT surface6 with LK‐

H052 45 mm

Vertical steps in DUT surface6 with LK‐

G32 25 mm

Optical surface properties diffuse reflective material of any color (white coating of

transparent and highly reflective material is recommend‐

ed)

Target Application dedicated to transducers (woofer, tweeter, micro‐speaker,

compression driver, headphone)



8.2 Scanning Hardware rev. 2.0


Sensor Non‐contact triangulation displacement sensor

Laser Protection Class Class II, eye‐safe, visible

CAUTION! Laser Radiation!

Avoid direct or indirect (e.g. reflection) exposure of hu‐

man eyes to beam.

Scanning Grid Polar coordinate system (, r), tangential triangulation

Vertical laser position (corresponds

with height profile which could be

measured)

z 0 310 mm

Free space between turn table and Z‐

axis‐frame (corresponds with height of

DUT5)

z 0 340 mm

Horizontal Shift (radius of circular area

scanned)

r 0 300 mm

Free space between stands (corre‐

sponds with Diameter of the DUT)5

d 760 mm

Angle of turntable 0 360 degree

Error in z position z 10 30 m

Error in r position r 10 30 m

Error in position 0.2 0.5 degree

Error in measured Geometry ( 0 < z < 10

mm)1 5 m

Scanning Speed2 0.3 1 points/s

Time for profile scan (50 points) 3 10 min

Time for explore scan (450 points) 3 1 h

Time for detailed scan (3200 points) 3 8 h

Time for geometry scan only (3200 points) 3 5 h

Working distance of

laser head, refer to

A2 Laser Displace‐

ment Sensor

Keyence LK‐G32 d 25 30 35 /

31.84

mm

Keyence LK‐G82 d 65 80 / 684 95 / 714 mm

Keyence LK‐

H052

d 40 50 60 mm

Sensor output ac‐displacement of target, distance to target

Lowest frequency displacement signal fmin 0 Hz



Highest frequency limit displacement

signal

fmax >fmin 10 25 kHz

Signal to Noise ratio3 SNR 30 dB

Noise level in displacement output3 xnoise m

Detection of optical errors Reliability check by correlating two measurement at dif‐

ferent distances and calculating S/N ratio

Stimulus used for excitation Shaped logarithmical sine sweep

Mechanical Protection Independent emergency stop if the laser head has me‐

chanical contact with target

Recommended workspace width w 85 cm

Recommended workspace depth d 61 80 cm

Recommended workspace height h 120 cm



Physical dimensions See following side and top view drawing

Mounting points for accessories

2 x M10 thread (pitch = 1.5) @ ø = 200

mm

2 x M10 thread (pitch = 1.5) @ ø = 300

mm

4 x 3/8” – 16 UNC thread @ ø = 330 mm

(Rev. >= 1.6)

M10 and 3/8” screws must not reach

through the turntable! Could cause

damages during movement of the turn‐

table.

Max. thread length inside turntable 10

mm.



Diameter of centering hole:

ø = 29.1H7 mm (29.1 +0.05/‐0 mm)

Diameter of centering piece

ø = 29.1H7 mm (29.1 +0/‐0.02 mm)

1 Laser sensor is kept on fixed vertical position and the vertical scanning range is limited by the peak‐to‐peak

value of the laser sensor. In this case the laser sensor determines the error of the measured geometry.

2 only positioning of the laser sensor (without vibration measurement)

3 depends on averaging, laser settings, target surface and stimulus

4 for measurements above fmax =10kHz

5 The DUT is placed on the turntable with the surface to be scanned on the upper side

6 A vertical step in the DUT surface above the specified maximum may cause:

A collision of the laser sensor with the DUT if H1 @ outer radius < H2 @ inner radius (step up)

Unmeasured points if H1 @ outer radius > H2 @ inner radius (step down), H = DUT height

8.3 Motor Control

Parameter Symbol Min Typ. Max Unit

Electrical Characteristics Stepper Motor Outputs

Output Voltage (peak to peak) Uout 24 V

Output Current (max) Iout 2 A

Output Current (adjusted for R‐ & Z‐

axis)

Iout 0.9 A

Output Current (adjusted for Phi‐

axis)

Iout 0.5 A

Recommended Operating Conditions

Power supply voltage VAC 100 240 V

Power AC‐frequency fAC 47 63 Hz

Operating ambient temperature TA 0 25 50 oC

Input power P 10 20 W

Primary power supply connection with protective earth conductor is required!

Power supply connection with removed earth contact could cause high voltages at the enclosure of the device.

8.4 Setup Parameter of Scanner




Scanning Grid

Increments of radius r rStep 0.02 1 mm

Minimal radius rmin 0 mm

Maximal radius rmax 300 mm

Increments in angle D 0.03 4.5 360 °

Manual grid control remove/add single radii

indicate critical radii (activate diving scanning

mode)

Vertical control mode Variable (normal)

Fixed (good for scanning of flat DUTs)

Minimal distance z > zmin (good for vacuum meas‐

urements)

Mark additional dangerous radii for safe scanning

Scanning Mode Vibration + Geometry

Geometry only

Generator / Signal Acquisition

Minimal Frequency fstart 0 < fend Hz

Maximal Frequency fend > fstart 10 25 kHz

Frequency Resolution f 23.44 Hz

Stimulus Shaping S 0 9 12 dB/oct

Maximal Voltage Umax 0 10 100 V

Averaging N 1 64 256

8.5 Vibration and Radiation Analysis (Results)

Parameter Comments Unit

Amplitude displacement transfer func‐

tion

Hx(f) for any cone point c(z,, r) for

Circular and radial vibra‐

tion mode

In‐phase component

Anti‐phase component

Quadrature component

dB (1 mm/V =

0dB)

3D Vibration Animation (Cone Surface) Enhanced cone vibration at frequency

f is superimposed with measured

geometry

Vibration can be decomposed in


Geometry and

vibration is rela‐

tive



tion mode




Color Mode:

Phase

Amplitude

(viewing angle and distance may be

changed, rotation and scaling of

DUT possible)

2D Vibration Magnitude and Phase Plot Magnitude and phase of vibration is

plotted versus projected geometry



tion mode




Color Mode:

phase

amplitude

Vibration is rela‐

tive but geometry

is in mm

2D Vibration Animation (Cone Profile at

) Enhanced cone vibration at frequency

f is superimposed with measured

cone profile at angle



tion mode




The transfer function H(f) of any cone

point can be selected

Geometry in mm,

vibration relative

Geometry of target surface Polar coordinates of cone point c(z,, r)

mm

Directivity plot () at frequency f in plane at for


tion mode




dB



Averaged () at frequency f for all

Total SPL response SPL(f) at field point r(ro,,) dB

SPL response of in‐phase component SPLin‐phase(f) at field point r(ro,,) dB

SPL response of anti‐phase component SPLanti‐phase(f) at field point r(ro,,) dB

SPL response of radial mode SPLradial(f) at field point r(ro,,) dB

SPL response of circular mode SPLcircular(f) at field point r(ro,,) dB

Total Acceleration Level Absolute summation of the cone ac‐

celeration. Scaled to be directly com‐

parable to SPL

dB

Acceleration Level of radial mode Cumulated acceleration of radial

mode

dB

Acceleration Level of circular mode Cumulated acceleration of circular

mode

dB

Acceleration Level of quadrature com‐

ponent

Cumulated quadrature acceleration dB

Acceleration Level of in‐phase compo‐

nent

Identical to In‐Phase SPL level dB

Acceleration Level of anti‐phase com‐

ponent

Identical to Anti‐Phase SPL level dB

8.6 Setup Parameter Analyzer


Frequency f fstart fend Hz

Distance to field point r ro m

Angle (off‐ axis) 0 360 degree

Angle (of the turn‐table) 0 360 degree

Decomposition Radial, circular modes

SPL related (In‐phase, Anti‐phase, Quadrature)

Color Modes Amplitude

Phase

Modeling Modes Sound Pressure Level

Acceleration Level

Amplitude Enhancement H ‐20 0 20 dB

Smoothing S 0 2 9 relative

Graphical Resolution 3200 50000 points

Period Time in Animation 0.1 1.5 10 seconds

Options (Checkbox) Mark interpolated points / mark sparse grid points

Scanning Vibrometer 9 Diagnostics C5


Increase visual grid resolution

Average directivity

9 Diagnostics

Visualize regular vibration modes The sound pressure output of axis‐symmetrical cones highly depends on the regular modes which propagate in radial di‐rection on the cone. The radial modes can be enhanced by using the decomposition technique. The measured behavior may be compared with the results predicted by axial‐symmetrical FEA to show

limits of the piston mode

first ring resonance, surround resonance,

bending modes

membrane modes

Total vibration modes

Radial modes only

Separate Vibration and Radiation Effects

The Total Acceleration Level compared to the Total Sound Pressure level summarizes the effect of the surface motion on the radiated sound.

KLIPPEL

40

50

60

70

80

90

102 103 104

SCN Result Curves

SP

L [dB

]

f [Hz]


The quadrature acceleration shows the vibration level which does not produce any sound at the receiver point. It compris‐es asymmetric motions, rocking and motion where the sur‐face vibration phase gets orthogonal to the radiated sound. The frequencies and quality of the mechanical modes can be found easily from the total acceleration level.

Analyze acoustical cancellation Acoustical cancellation occurs when the volume flow q of the

cone area vibrating in phase with the total sound gets close to

the volume flow of the area vibrating 180° phase shifted.



KLIPPEL

40

45

50

55

60

65

70

75

80

85

90

2*102 4*102 6*102 8*102 103 2*103 4*103 6*103 8*103

SCN Result Curves

SP

L [

dB

]

f [Hz]

Total SPL In-Phase Component Anti-Phase Component

If the in‐phase and anti‐phase components get close to each other, there will be a strong dip in the produced sound pres‐sure at the receiver point. A design goal of good loudspeakers should be to always keep a certain minimal distance between both components to avoid acoustical cancellation effects.

Visualize irregular vibration behav‐ior

Flexible wires and irregularities in the geometry (e.g. cone thickness) and density of the material may cause significant circular modes on the cone. These modes may be enhanced by viewing the circular modes only (Decomposition method).

Diaphragm of a horn compression drivers with irregular thick‐ness

Anisotropic materials Some material used for loudspeaker cones and diaphragms have anisotropic properties which produce a vibration pattern that depends on the direction. For example, the vibration of the Kevlar cone becomes maximal in the direction of the fi‐bers.

Localize Cause of Nonlinear Distor‐tion

If cone or surround displacement is high compared to the geometry the cone behaves nonlinearly and produces nonlin‐ear distortion of the output signal. Analysis: At critical excitation frequency search for regions of



maximal displacement in the 3D surface animation or 2D pro‐file animation. Target: Reduce the Quadrature and anti‐phase vibration components which do not contribute to the SPL but generate nonlinear distortion. Remedy: Investigate design choices (different geometry and material) by using FEA

r = 41.0 mm, phi = 49.5°

The first bending anti‐resonance produces high displacement and large bending moments at the outer rim of the cone.

Rocking Modes Rocking modes can easily be detected by looking at the quad‐rature acceleration level.

KLIPPEL

40

45

50

55

60

65

70

75

80

85

90

103 104

SCN Result Curves

SP

L [

dB

]

f [Hz]


If the surface vibrates as a rigid body the quadrature compo‐nent is very small. A rocking motion does not produce much radiated sound but contains substantial vibration energy. This leads to a peak in acceleration level (in the example at 470Hz and 540Hz) After setting the cursor to the critical frequency 470 Hz the rocking mode in the picture below may be identified.

r = 20.0 mm, phi = 270.0° Diaphragm of a horn compression driver performing rocking mode and causing rub&buzz problems.

Scanning Vibrometer 10 Evaluation C5


10 Evaluation

Measurement

Service

The Vibrometer and Analysis Software may be evaluated by sending a transduc‐er to KLIPPEL GmbH (ask for details [email protected]). After performing a detailed scan the results (vibration + geometry) and the SCN Analysis Software will be provided for evaluation (animation, visualization, SPL response, directivi‐ty, decomposition). Besides a Windows PC no hardware is required.

11 References

Papers [1] W. Klippel, J. Schlechter, “Measurement and Visualization of Loudspeaker Cone Vibration”, presented at the 121st Convention of the AES in San Francisco, CA, USA, 2006, October 5‐8. [2] W. Klippel, J. Schlechter, “Distributed Mechanical Parameters of Loudspeak‐ers 1: Measurements”, JAES Volume 67, Issue 7/8 pp. 600‐611, July 2009 [3] W. Klippel, J. Schlechter, “Distributed Mechanical Parameters of Loudspeak‐ers 2: Diagnostics”, JAES Volume 67, Issue 9 pp. 696‐708, September 2009 [4] W. Klippel, J. Schlechter, “Dynamical Measurement of the Effective Radiation Area SD”, presented at the 128th Convention of the AES in London, UK, 2010, May 22‐25.

Application Notes Cone Vibration and Radiation Diagnostics, Application Note AN31 Effective Radiation Area SD, Application Note AN32

Manual SCN Vibrometer, Manual of the Klippel R&D System, 2011

Find explanations for symbols at:

http://www.klippel.de/know‐how/literature.html

Last updated: July 04, 2019

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